1. Field of the invention
The present invention relates to a pneumatic tool, such as a pneumatic nailer that has a driver for driving fasteners.
2. Description of the Related Art
U.S. Pat. No. 3,438,449 teaches a pneumatic nailer that has a driver for driving nails. The nail is set in the nailer in a position adjacent a front end of a driver and is then driven into a workpiece with a multiple of impact blows by the driver. FIG. 4 of this U.S. patent has been incorporated into the drawings of this application as FIG. 19. FIG. 19 shows a nailer 100 in a non-operative position, in which compressed air is supplied from a pressurized air source (not shown) to a pressure accumulation chamber 101 via an air hose 107, so that the compressed air is accumulated within the presssure accumulation chamber 101. The pressure accumulation chamber 101 communicates with a variable pressure chamber 103 via a port 102. The variable pressure chamber 103 is defined between a lower end of a sleeve valve 104 and a top surface of a flange 105a of a cylinder 105. In the non-operative position shown in FIG. 19, ports 108 connecting the variable pressure chamber 103 to a lower piston chamber 111 are positioned between an upper seal ring 110a and a lower seal ring 110b, so that the variable pressure chamber 103 is disconnected from the lower piston chamber 111.
On the other hand, because of the pressure of the compressed air accumulated within the variable pressure chamber 103, the sleeve valve 104 is lifted upward. As a result, the upper end of the sleeve valve 104 is pressed against a seal member 112. Further, an upper piston chamber 113 is disconnected from the pressure accumulation chamber 101. Here, the upper piston chamber 113 opens to the outside via a central opening 115a of a cylinder cap 115 and exhausting slots 151 formed in a housing 150. The cylinder cap 115 is secured to the upper end of the cylinder 105.
The lower piston chamber 111 opens to the outside via a port that is formed by a flat surface portion 120a of a driver 120, which driver serves to drive nails.
In the non-operative position shown in FIG. 19, an operator sets a nail (not shown) in a position adjacent the front end of the driver 120. Then, the operator presses the nailer 100 downward against a workpiece, so that the piston 110 with the driver 120 moves upward relative to the cylinder 105. When the lower seal ring 110b of the piston 110 has moved to a position above the ports 108, the lower piston chamber 111 communicates with the variable pressure chamber 103, so that the compressed air is supplied to the lower piston chamber 111. At the same time, the port previously formed by the flat surface portion 120a of the driver 120 is closed by a bumper 121, so that the lower piston chamber 111 is disconnected from the outside.
With the compressed air supplied to the lower piston chamber 111, the piston 110 with the driver 120 abruptly moves upward. Then, a protrusion 110c on the upper surface of the piston 110 moves to engage the central opening 115a, so that the upper piston chamber 113 is disconnected from the outside. As the piston 110 moves upward, the air within the upper piston chamber 113 is compressed.
The piston 110 abuts the cylinder cap 115 when it moves further upward to compress the air within the upper piston chamber 113 as described above. The piston 110 moves further upward with abutment to the cylinder cap 115 so as to also move the cylinder cap 115 upward. As a result, the cylinder 105 moves upward. As the cylinder cap 115 thus moves upward, the central opening 115a receives a protrusion 152 formed on an inner wall of the upper portion of the housing 150, so that the upper piston chamber 113 is substantially disconnected from the atmosphere.
On the other hand, as the cylinder 105 with the cylinder cap 115 moves upward, the lower piston chamber 111 opens to the outside via openings 114. At the same time that the lower piston chamber 111 opens to the atmosphere, the variable pressure chamber 103 also opens to the outside via the ports 108. Although the ports 108 are plural in number and are circumferentially spaced from each other, the port 102 that connects the variable pressure chamber 103 to the accumulation chamber 101 is one in number. Therefore, the sectional area of the whole ports 108 is substantially greater than the sectional area of the port 102. As a result, the pressure within the variable pressure chamber 103 abruptly drops.
The pressure within the upper piston chamber 113 increases while the pressure within the variable pressure chamber 103 drops as described above. Therefore, the increased pressure applied to the upper end of the sleeve valve 104 forces the sleeve valve 104 to move downward. As the sleeve valve 104 moves downward, the lower end of the sleeve valve 104 is pressed against the upper surface of the flange 105a of the cylinder 105. Also, as the sleeve valve 104 moves downward, the upper end of the sleeve valve 104 moves apart from the seal member 112. As a result, the upper piston chamber 113 communicates with the accumulation chamber 101. Therefore, the compressed air is supplied to the upper piston chamber 113 to move the piston 110 downward.
During the supply of the compressed air to the upper piston chamber 113, the cylinder 105 with the cylinder cap 115 further moves upward. On the other hand, the driver 120 moves downward with the piston 110 to apply an impact blow to the nail.
Because the lower end of the sleeve valve 104 abuts the flange 105a of the cylinder 105, the sleeve valve 104 moves upward with the cylinder 105. Therefore, the upper end of the sleeve valve 104 subsequently abuts the seal member 112 to disconnect the upper piston chamber 113 from the accumulation chamber 101.
When the piston 110 reaches the lower stroke end, the lower seal ring 110b returns to a position below the ports 108, so that the compressed air is supplied to the variable pressure chamber 103 from the accumulation chamber 101 via the port 102.
On the other hand, as the piston 110 moves downward, the protrusion 110c is removed from the central opening 11 Sa of the cylinder cap 115, so that the upper piston chamber 113 opens to the outside via the central opening 115a and the opening 151. As a result, the pressure within the upper piston chamber 113 is lowered. Although, at this stage, the protrusion 152 of the housing 150 engages the central opening 115a, the central hole 150 may not be completely closed by the protrusion 152. Therefore, the compressed air within the upper piston chamber 113 may be gradually exhausted to the outside via the central opening 115a and the opening 151.
The upper piston chamber 113 thus opens to the outside while the variable pressure chamber 103 is disconnected from the lower piston chamber 111 to cause increase of the pressure therewithin. The increased pressure within the variable pressure chamber 103 is applied to the flange 105a to lower the cylinder 105. Consequently, one cycle of the operation of the nailer 100 is completed.
The above operation is again performed as the operator again presses the nailer 100 against the workpiece, so that the nail can be driven into a workpiece with a multiple of impact blows by the driver 120.
However, as shown in FIG. 19, the nailer 100 of the U.S. patent has a short stroke length in comparison with the diameter of the housing 150. Therefore, the nailer 100 cannot be effectively used at a narrow workplace. The housing 150 may have a long and narrow configuration if the stroke length is long. However, the following problems may be produced if such a long stroke length has been incorporated into the nailer 100:
As described above, when the variable pressure chamber 103 opens to the outside while the pressure within the upper piston chamber 113 increases, the sleeve valve 104 moves downward. The lower end of the sleeve valve 104 then abuts the flange 105a of the cylinder 105. The compressed air is supplied to the upper piston chamber 113, so that the sleeve valve 104 is moved upward together with the cylinder 105. The sleeve valve 104 subsequently abuts the seal member 112 to disconnect the upper piston chamber 113 from the accumulation chamber 101.
If the stroke length of the piston 110 is long, the sleeve valve 104 may move upward before the piston 110 reaches the lower stroke end. As a result, the compressed air may not be sufficiently supplied to the upper piston chamber 113. The impact force applicable to the nail by the driver 120 may therefore be weakened. In addition, the operation of the driver 120 becomes unstable.